In a Universe where change typically occurs over eons, astronomers have been given a rare front-row seat to watch as the small, icy world beyond Saturn builds an entirely new set of rings in real time.
A team of astronomers in Brazil discovered that bands of material orbiting around (2060) Chironthe 125-mile (200-kilometer) wide object that orbits the sun between Saturn and Uranus is new and still taking shape. The findings suggest that the area around Chiron is in a transition state somewhere between a chaotic debris cloud and a fully formed ring system, giving scientists a rare snapshot of the ring formation process that has never been directly observed before.
Chiron joins asteroid Chariklo and dwarf planets Haumea And Quaoar as one of four small ringed worlds in our solar system, but perhaps the most dynamic of all.
Chiron's changing environment, detailed in an article published Oct. 14 in the journal Letters in an astrophysical journalcould help scientists understand how small icy objects, as well as giant planets such as Saturn and Uranus, built their iconic rings billions of years ago.
Rings in the making
Composed of rock, water ice and organic compounds, Chiron belongs to a strange population of objects called centaurs, which orbit between Jupiter and Neptune and behave partly like an asteroid and partly like a comet. Chiron orbits the Sun once every 50 Earth years.
Since its discovery in 1977, astronomers have watched it become brighter and brighter from time to time. even grow a weak tailindicating that it sometimes spews gas and dust into space.
In September 2023, when Chiron briefly passed in front of a distant star from Earth's perspective, the Pico dos Díaz Observatory in Brazil detected tiny, repeating dips in the star's light. When the researchers compared these data with similar events cataloged in 2011, 2018 and 2022, they found that three separate dense rings orbiting approximately 170–270 miles (270–430 km) from Chiron's center remained in place for more than a decade.
In the 2023 data, the team also discovered a new disk-shaped structure ranging from 120 to 500 miles (200 to 800 km) around Chiron that was not present in the previous data. The wider diffuse disk likely formed only within the last decade, perhaps as a result of a collision or flare that released fresh material into orbit, Pereira said.
Interestingly, the team also discovered a faint outer feature nearly 870 miles (1,400 km) from Chiron—well beyond the so-called Roche limit, the boundary where ring material should clump together into the moon rather than remain as debris, the new study notes.
“This is the first time we have found any evidence of material in this region,” Pereira told Live Science, adding that higher resolution observations are needed to confirm this. “Beyond this limit, the particles forming the ring should naturally start to coalesce into a satellite, but something appears to be preventing this from happening.”
Researchers aren't sure what caused Chiron's strange situation. One possibility is that the volatile ice beneath its surface exploded in a cometary flare, spewing out dust and ice that later settled in orbit. Another reason is that a small moon crashed, scattering fragments that spread along Chiron's equator, according to a new study.
The latter theory could also explain Chiron's steady increase in brightness over the past decade, which is difficult to explain by cometary activity alone, Pereira said.
Other experts say the findings raise new questions about how rings around small bodies can persist for long periods of time.
“Perhaps something is adding energy to these particles and allowing them to persist beyond the limit without merging.” Kayleigh Rockcliffepostdoctoral researcher at NASA Goddard Space Flight Center in Maryland, which was not involved in the new paper, told Live Science by email.
It's also possible that the ring is very scattered or simply hasn't been around long enough to merge, Rockcliffe said. “Maybe it formed recently and hasn't had a chance to form a little centaur yet.”
To confirm whether Chiron's rings are actually evolving and not just appearing different from our changing perspective, astronomers hope to capture more events in which Chiron passes in front of distant stars. Such events, recorded by high-speed cameras at observatories on several continents, are the only direct way to see whether the opacity, width or position of disk material is changing—signs that Pereira said could show dust and ice are actively being redistributed, offering direct evidence of ongoing evolution.
“However, the ideal scenario to satisfy our curiosity would be a space mission dedicated to observing this intriguing system in situ,” Pereira said.
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